The chemical reaction of chlorine with alkylbenzenes, such as toluene, to prepare nuclear substituted chloro-compounds such as monochlorotoluene, is well known and of considerable commercial importance. Such reactions are generally carried out in the presence of a chlorination catalyst such as antimony chloride, ferric chloride, aluminum chloride, and the like. The usual products of such reactions are a mixture of various mono-chlorinated and/or polychlorinated compounds and various positional isomers of these. For example, in the liquid phase substitution-chlorination of toluene by reaction of chlorine and toluene, to form monochlorotoluene, the usual product is a mixture of orthochlorotoluene and parachlorotoluene which may, in addition, contain varying amounts of other chlorinated products such as metachlorotoluene, dichlorotoluene, polychlorotoluenes and benzylic chlorides. Of the major reaction products, that is orthochlorotoluene and parachlorotoluene, the latter is the most commercially valuable. In the past, considerable effort has been expended in attempts to direct the chlorination reaction in such a manner as to lower the ratio of orthochlorotoluene to parachlorotoluene, that is, to discover reaction conditions under which the formation of parachlorotoluene is favored. Thus, for example, it is known from U.S. Pat. No. 1,946,040 that when alkylbenzenes are reacted with chlorine, the yield of parachlorinated product is improved with the aid of a mixed catalyst comprising sulfur and antimony trichloride and, optionally, iron or lead. In British Pat. No. 1,153,746 (1969) it is disclosed that in the chlorination of toluene in the presence of a ring chlorination catalyst, such as ferric chloride, antimony chloride, and the like, the ratio of orthochloro to parachloro isomers produced may be lowered by the presence of an organic sulfur compound such as thiophene, hexadecylmercaptan, dibenzothiophene or the like. Furthermore, in British Pat. No. 1,163,927 (1969) it is disclosed that the proportion of parachlorotoluene produced may be improved when toluene is chlorinated in the presence of elemental sulfur or an inorganic sulfur compound and a ring-chlorination catalyst such as ferric chloride, aluminum chloride, antimony chloride, zinc chloride, iodine, molybdenum chloride, stannous chloride, zirconium tetrachloride or boron trifluoride. In U.S. Pat. No. 3,226,447, issued Dec. 28, 1965 to Bing et al, it is disclosed that in the substitution - chlorination of benzenes and toluene by chlorine, the ratio of ortho isomer to para isomer in the chlorinated product may be lowered when the reaction is carried out in the presence of an iron, aluminum or antimony halide catalyst and a co-catalyst which is an organic sulfur compound wherein the sulfur is divalent. Examples of such co-catalysts include various mercaptans, mercapto-aliphatic carboxylic acids, aliphatic thiocarboxylic acids, alkyl sulfides, alkyl disulfides, thiophenols, aryl sulfides, aryl disulfides and the like containing divalent sulfur. Although improvements in the yield of parachloroalkylbenzenes may be achieved by means of the various prior art processes, it will be appreciated that still further improvements, especially through the use of more effective para-directing catalysts are desirable.
It is an object of this invention to provide a process for the directed nuclear chlorination of alkylbenzenes whereby the formation of parachloroalkylbenzenes is substantially increased. It is a further object to provide new catalysts for the para-directed halogenation of aromatic compounds, especially alkylbenzenes. These and other objects and advantages of this invention will be apparent from the following description of the present invention.